If the reason you don't want to use a toothpick is that it leaves a big hole, you can buy a cheap little item called a cake tester that is just a thin piece of wire with a little handle. It leaves such a small hole that as to be unnoticeable. As a bonus, it is quite useful for checking the doneness of vegetables. This is the one I use.

In the same spirit of using an alternate thing to poke the cake with, I typically either use a skewer (as they're longer, so you're sure they got to the middle), or some uncooked strand of thin pasta (vermicelli, linguini, spaghetti)
–
JoeAug 4 '10 at 2:41

Not all recipes specify the doneness internal temperature. Alton Brown usually include the temperature, so look at his recipes to get a feeling for the correct ball park. In this recipe for carrot cake, the recipe reads: If you have a thermometer, you are looking for an internal temperature of 205-210 degrees. noblepig.com/2010/01/15/alton-browns-18carrot-cake.aspx
–
soegaardAug 4 '10 at 21:52

1

The temperature for doneness is 98 degreee celsius. This is the temperature that Corriher repeatedly uses in her book BakeWise.
–
soegaardDec 12 '10 at 15:48

Possibly this answer came in before the answer was editing to specify a non-penetrative method.
–
Chris SteinbachJan 9 '13 at 15:13

Yes. The current version of the question even states that "I like the thermometer idea".
–
soegaardJan 9 '13 at 20:19

I always wiggle the cake a bit to see if the top moves. If it is undone the top with wiggle like it's wet. If done, it should be firm. If you know your oven well, the timing should be a good estimate too, and then use the wiggle method.

The top can firm up, while the center's still gooey, so this isn't always the best method. It's not bad if it's a recipe you've done before, but if the oven's too hot, the top might set up too early.
–
JoeAug 4 '10 at 2:39

As is the case for all eye-ball recommendations, you need to use complimentary methods. That is why I mentioned the time point. But yes, this is definitely an estimate and should be used as a supplement to other methods.
–
nicorelliusAug 4 '10 at 21:58

poke a wooden toothpick into the center of a cake; if it comes out with wet batter, keep cooking; if it comes out clean and dry, contrary to common knowledge, it's probably overcooked; if it comes out with a few crumbs stuck to it, it's probably perfect.